pgadmin4-np: Silent user install support (#354)

Refresh of installer arguments in order to:

* support silent installs in both user and global contexts => `SUPPRESSMSGBOXES` will let the installer assume local user install
if it does not have admin rights instead of asking for elevated privileges

* get rid of a post_install error in case of local user install 
(because 'pgAdmin 4' folder can't be located under the common
start menu) by using `NOICONS` during install instead of 
trying to remove start menu icons after the fact

bucket/pgadmin4-np.json

@@ -11,19 +11,23 @@
     },
     "installer": {
         "args": [
-            "/verysilent",
-            "/nocancel",
-            "/norestart",
-            "/dir=$dir"
+            "/VERYSILENT",
+            "/SUPPRESSMSGBOXES",
+            "/SP-",
+            "/NOCANCEL",
+            "/NORESTART",
+            "/NOICONS",
+            "/DIR=$dir"
         ]
     },
-    "post_install": "Remove-Item -Recurse \"$([Environment]::GetFolderPath('commonstartmenu'))\\Programs\\pgAdmin 4\"",
     "uninstaller": {
         "file": "unins000.exe",
         "args": [
-            "/verysilent",
-            "/nocancel",
-            "/norestart"
+            "/VERYSILENT",
+            "/SUPPRESSMSGBOXES",
+            "/SP-",
+            "/NOCANCEL",
+            "/NORESTART"
         ]
     },
     "bin": [